This invention concerns improvements in or relating to reflection holograms and relates more particularly to a method of and apparatus for making reflection holograms (sometimes conversely called holographic reflectors), and reflection holograms made by use of such method and apparatus.
Reflection holograms can provide efficient colour reflective filters which reflect a narrow waveband of incident light. A reflection hologram can be made by scanning a light beam, usually from a laser, over the surface of a photosensitive film behind which is a mirror. The incident beam and the beam reflected back from the mirror produce interference fringes in the film which, usually after suitable processing, provide corresponding variations in refractive index that give rise to the hologram. Such a method is disclosed in UK Pat. No. GB2071866B in which scanning of the laser beam is effected by two mirrors arranged to rotate about respective axes so as to produce horizontal and vertical movement. However, there is some limitation on the forms of hologram which can be satisfactorily produced by use of such mirror arrangement.